Download App

Moving Charges and Magnetism — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsMoving Charges and Magnetism3 Marks
Question
Write the expression for the magnetic moment ($\overrightarrow{\text{m}}$) due to a planar square loop of side ‘l’ carrying a steady current I in a vector form. In the given figure this loop is placed in a horizontal plane near a long straight conductor carrying a steady current $I_1$ at a distance l as shown. Give reasons to explain that the loop will experience a net force but no torque. Write the expression for this force acting on the loop.
✓

Answer

$\overrightarrow{\text{m}} = \text{I}\overrightarrow{\text{A }} ( \overrightarrow{\text{A}} = \text{ area vector) }$
Torque: The magnetic field due to the long current carrying wire is perpendicular to the plane of paper. Hence the force acting on each of the four sides is in the plane of the paper and the net torque is zero.
Alternate Answer
$\overrightarrow{\text{m}}$is perpendicular to the plane of paper and$\overrightarrow{\text{B}}$ is perpendicular to the plane of paper. Hence $\overrightarrow{\tau} =\overrightarrow{\text{m}}\times\overrightarrow{\text{B}} = 0 $
Force:
Force on upper horizontal side $ = \frac{\text{I}l\mu_{o}\text{I}_{1}}{2\pi\text{l}} =\frac{\text{I}\mu_{o}\text{l}_{1}}{2\pi}\text{ (attractive) }$
Force on lower horizontal side $ = \frac{\text{I}l\mu_{o}\text{I}_{1}}{2\pi(2l)} = \frac{\text{I}\mu_{o}\text{I}_{1}}{4\pi}\text{ (repulsive)}$
The direction of these forces being opposite to each other therefore net force $ = \frac{\mu_{o}\text{I}_{1}\text{I}}{4\pi}\text{ (attractive) }$
(The net force on the two vertical sides is zero)
Torque: The magnetic field due to the long current carrying wire is perpendicular to the plane of paper. Hence the force acting on each of the four sides is in the plane of the paper and the net torque is zero.

Alternate Answer
$\overrightarrow{\text{m}}$is perpendicular to the plane of paper and$\overrightarrow{\text{B}}$ is perpendicular to the plane of paper. Hence $\overrightarrow{\tau} =\overrightarrow{\text{m}}\times\overrightarrow{\text{B}} = 0 $
Force: Award this mark irrespective of result obtained or calculation done by the students.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "3 Marks Question" from Moving Charges and Magnetism→Moving Charges and Magnetism — all question types→Physics STD 12 Science question papers→Gujarat Board STD 12 Science question papers→Gujarat Board question paper generator→

Similar questions

Explain briefly the process of charging a parallel plate capacitor when it is connected across a d.c. battery. A capacitor of capacitance ‘C’ is charged to ‘V’ volts by a battery. After some time the battery is disconnected, and the distance between the plates is doubled. Now a slab of dielectric constant, 1 < k < 2, is introduced to fill the space between the plates. How will the following be affected:
  1. The electric field between the plates of the capacitor.
  2. The energy stored in the capacitor.
Justify your answer by writing the necessary expressions.
→
The following table gives the output of a two input logic gate.
  1. Identify the logic gate and draw its logic symbol.
  2. If the output of this gate is fed as input to a NOT gate, name the new logic gate so formed.
A
B
Y
0
0
1
1
0
1
0
1
1
1
1
0
→
A light ray, going through a prism with the angle of prism 60°, is found to deviate by 30°. What limit on the refractive index can be put from these data?
→
The equation for the vibration of a string, fixed at both ends vibrating in its third harmonic, is given by$\text{y}=(0.4\text{cm})\sin\big[(0.314\text{cm}^{-1})\text{x}\big]\cos\big[(600\pi\text{s}^{-1})\text{t}\big]$
  1. What is the frequency of vibration?
  2. What are the positions of the nodes?
  3. What is the length of the string?
  4. What is the wavelength and the speed of two travelling waves that can interfere to give this vibration ?
→
Sketch the graph showing variation of stopping potential with frequency of incident radiations for two photosensitive materials A and B having threshold frequencies $v_{A >}v_{B.}$​​​​​​​
  1. In which case is the stopping potential more and why?
  2. Does the slope of the graph depend on nature of the material used? Explain.
→
Figure shows a cart. Complete the table shown.
→
Obtain expression $\vec{J}=\sigma \vec{E}$ of Ohm's law on the basis of drift velocity.
→
The sunlight reaching Earth has maximum electric field of $810Vm^{-1}.$ What is the maximum magnetic field in this light?
→
A uniformly moving train passes by a long platform. Consider the events' engine crossing the beginning of the platform' and 'engine crossing the end of the platform'. Which frame (train frame or the platform frame) is the proper frame for the pair of events?
→
Name the parts of the electromagnetic spectrum which is:
  1. Suitable for radar systems used in aircraft navigation.
  2. Used to treat muscular strain.
  3. Used as a diagnostic tool in medicine.
Write in brief, how these waves can be produced.
→